Three dimensional digitizing devices, which obtain a representation of the surface of an object, are used in a variety of fields. In particular, such devices are commonly used in areas requiring computer modeling and computer-aided design of objects. These digitizers may be used to replace techniques such as casting which typically are less accurate and require significant time and expertise to perform.
Three dimensional digitizing devices may be divided roughly into four areas: mechanical contact, magnetic, ultrasonic and digital imaging. In the dental field, commercially available systems for computer-aided fabrication of dental restorations utilize either mechanical contact or digital imaging digitizing devices. These commercially available systems are described and compared in "Dental CAD-CAM Systems-What is the state of the art?" JADA, vol. 122, December 1991, pages 43-48, by E. Dianne Rekow. Another commercial system, though not suitable for use in a dental environment, is a mechanical contact, three-dimensional digitizer called the Space Tablet and the Perceptor 3D, introduced by Micro Control Systems (Vernon, Conn.).
A number of other digitizing systems were referred to in the related application Ser. No. 07/682,001 now U.S. Pat. No. 5,131,844 issued Jul. 21, 1992. Additional systems of background interest are also disclosed in U.S. Pat. Nos. 5,017,139 (Mushabac) and 4,997,369 (Shafir). See also U.K. Patent Application No. 2,140,308A.
Mechanical systems are typically advantageous over optical systems because of their relative simplicity, and hence reduced cost. However, all of the aforementioned mechanical contact systems face the problem of determining when the contact digitizer is, in fact, in contact with the surface of the sampled object. To solve this problem, most systems rely on additional electronic circuitry or mechanical structure as part of the contact digitizer to insure that any points obtained are in fact on the surface of the sampled object. For example, the "DentiCAD System" as described in the aforementioned article by Rekow, relies on having a bias current flowing through the tooth, or sampled object, when the object is being sampled. Current flows only when the probe tip is in contact with the surface of the tooth. As another example, Shafir (U.S. Pat. No. 4,997,369) relies on a Wheatstone bridge and a supplemental computer program to determine whether the object is in fact in contact with the probe tip.
Accordingly, it is an object of the present invention to provide a system and method for obtaining a digitized representation of a surface of an object using a mechanical contact probe without the need for additional circuitry or mechanical structure.
It is another object of the invention to provide a system and method for guiding an operator through the process of sampling an object.